Protocols for RS485

Ian McCrum · Joined: 26 Oct 2003 Posts: 14 Location: Northern Ireland

A ling time ago, I implemented several RS485 networks using a Master-Slave approach, slow baud rates, delays to allow line turnaround, resistors to bias the line to avoid false startbits when all drivers are tristate. These worked fine...

I typically use 4 wires and have a PC as the master, this allows use of hyperterminal for testing, I use pure ASCII and a "lline of text" at the heart of the protocol.

I am hoping to play with an embedded linux board talking to lots of "cable bulges" , the cable bulge will be PICs.

I wonder if there is information anywhere on actuak RS485 protocols in common use? presumably various fieldbuses are documented. If I recall correctly, the original Apple Macintosh network (localtalk?) used RS485.

Does anyone have any docs on actual RS485 LANs?
tia
Ian McCrum
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Ian McCrum, email address held at
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Humberto · Posted: Sun Nov 14, 2004 6:54 pm

Hi Ian,

Ian McCrum · Joined: 26 Oct 2003 Posts: 14 Location: Northern Ireland

Many thanks, the URL was just what I was looking for.

On reflection I need to find a LLC and MAC that suits RS485 and works with the network layers and above of TCP/IP ( which I know and love)

... a quick hack may well work but there must be a better way.

I'll study the appletalk data (and a datasheet on the Zilog 8230) to see if it makes sense. ( the linux end should not be a problem and apple did support 6502s running apple/local talk)

Very kindest regards
Ian
_________________
Ian McCrum, email address held at
www.eej.ulst.ac.uk/~ian